Development of a Flying Robot With a Pantograph-Based Variable Wing Mechanism

We develop a flying robot with a new pantograph-based variable wing mechanism for horizontal-axis rotorcrafts (cyclogyro rotorcrafts). A key feature of the new mechanism is to have a unique trajectory of variable wings that not only change angles of attack but also expand and contract according to wing positions. As a first step, this paper focuses on demonstrating the possibility of the flying robot with this mechanism. After addressing the pantograph-based variable wing mechanism and its features, a simulation model of this mechanism is constructed. Next, we present some comparison results (between the simulation model and experimental data) for a prototype body with the proposed pantograph-based variable wing mechanism. Both simulation and experimental results show that the flying robot with this new mechanism can generate enough lift forces to keep itself in the air. Furthermore, we construct a more precise simulation model by considering rotational motion of each wing. As a result of optimizing design parameters using the precise simulation model, flight performance experimental results demonstrate that the robot with the optimal design parameters can generate not only enough lift forces but a 155 gf payload as well

FUNDAMENTAL UNDERSTANDING OF THE CYCLOIDAL-ROTOR CONCEPT FOR MICRO AIR VEHICLE APPLICATIONS

The cycloidal-rotor (cyclorotor) is a revolutionary flying concept which has not been systematically studied in the past. Therefore, in the current research, the viability of the cyclorotor concept for powering a hover-capable micro-air-vehicle (MAV) was examined through both experiments and analysis. Experimental study included both performance and flow field measurements on a cyclorotor of span and diameter equal to 6 inches. The analysis developed was an unsteady large deformation aeroelastic analysis to predict the blade loads and average aerodynamic performance of the cyclorotor. The flightworthiness of the cyclorotor concept was also demonstrated through two cyclocopters capable of tethered hover. Systematic performance measurements have been conducted to understand the effect of the rotational speed, blade airfoil profile, blade flexibility, blade pitching amplitude (symmetric and asymmetric blade pitching), pitching axis location, number of blades with constant chord (varying solidity), and number of blades at same rotor solidity (varying blade chord) on the aerodynamic performance of the cyclorotor. Force measurements showed the presence of a significant sideward force on the cyclorotor (along with the vertical force), analogous to that found on a spinning circular cylinder. Particle image velocimetry (PIV) measurements made in the wake of the cyclorotor provided evidence of a significant wake skewness, which was produced by the sideward force. PIV measurements also captured the blade tip vortices and a large region of rotational flow inside the rotor. The thrust produced by the cyclorotor was found to increase until a blade pitch amplitude of 45 was reached without showing any signs of blade stall. This behavior was also explained using the PIV measurements, which indicated evidence of a stall delay as well as possible increase in lift on the blades from the presence of a leading edge vortex. Higher blade pitch amplitudes also improved the power loading (thrust/power) of the cyclorotor. When compared to the flat-plate blades, the NACA 0010 blades produced the highest values of thrust at all blade pitching amplitudes. The NACA blades also produced higher power loading than the flat plate blades. However, the reverse NACA 0010 blades produced better power loadings at lower pitching amplitudes, even though at high pitch amplitudes, regular NACA blades performed better. Among the three NACA sections (NACA 0006, NACA 0010 and NACA 0015) tested on the cyclorotor, NACA 0015 had the highest power loading followed by NACA 0010 and then NACA 0006. The power loading also increased when using more blades with constant chord (increasing solidity); this observation was found over a wide range of blade pitching amplitudes. Asymmetric pitching with higher pitch angle at the top of the blade trajectory than at the bottom produced better power loading. The chordwise optimum pitching axis location was approximately 25-35% of the blade chord. For a constant solidity, the rotor with fewer number of blades produced higher thrust and the 2-bladed rotor had the best power loading. Any significant bending and torsional flexibility of the blades had a deleterious effect on performance. The optimized cyclorotor had slightly higher power loading when compared to a conventional micro-rotor when operated at the same disk loading. The optimum configuration based on all the tests was a 4-bladed rotor using 1.3 inch chord NACA 0015 blade section with an asymmetric pitching of 45 at top and 25 at bottom with the pitching axis at 25% chord. The aeroelastic analysis was performed using two approaches, one using a second-order non-linear beam FEM analysis for moderately flexible blades and second using a multibody based large-deformation analysis (especially applicable for extremely flexible blades) incorporating a geometrically exact beam model. An unsteady aerodynamic model is included in the analysis with two different inflow models, single streamtube and a double-multiple streamtube inflow model. For the cycloidal rotors using moderately flexible blades, the aeroelastic analysis was able to predict the average thrust with sufficient accuracy over a wide range of rotational speeds, pitching amplitudes and number of blades. However, for the extremely flexible blades, the thrust was underpredicted at higher rotational speeds and this may be because of the overprediction of blade deformations. The inclusion of the actual blade pitch kinematics and unsteady aerodynamics was found crucial in the accurate sideward force prediction

A Simple Passive Attitude Stabilizer for Palm-size Aerial Vehicles

This paper presents a simple passive attitude stabilizer (PAS) for vision-based stabilization of palm-size aerial vehicles. First, a mathematical dynamic model of a palm-size aerial vehicle with the proposed PAS is constructed. Stability analysis for the dynamics is carried out in terms of Lyapunov stability theory. The analysis results show that the proposed stabilizer guarantees passive stabilizing behavior, i.e., passive attitude recovering, of the aerial vehicle for small perturbations from a stability theory point of view. Experimental results demonstrate the utility of the proposed PAS for the aerial vehicle

Nonlinear Aeroelastic Coupled Trim Modeling Of Cycloidal Rotor Based Micro Air Vehicle

Present generation of hover-capable micro air vehicles (MAVs) based on conventional rotors have shown poor performance in terms of endurance (<15 minutes), agility, and disturbance-rejection capability. Developing next generation of MAVs would require radical improvements in propulsion systems as well as control and guidance strategies. Cycloidal rotor is one such novel propulsion concept, which has huge potential due to its higher efficiency and maneuverability (instantaneous 360° thrust vectoring capability). Cycloidal rotor is a horizontal-axis rotary wing system which utilizes cyclic blade pitching to generate lift and thrust. A crucial step towards building efficient MAVs utilizing cycloidal rotor systems involves developing an aeroelastic framework and a coupled trim methodology, which could be utilized for design optimization and this is the main objective of the present dissertation. To obtain instantaneous blade aerodynamic forces and performance (cycle-averaged thrust and power) of cycloidal rotor, an unsteady aerodynamic model is developed. Towards this, aerodynamics of cycloidal rotor is investigated thoroughly and various underlying physical phenomena such as dynamic virtual camber, effects of near and shed wake, leading edge vortices are rigorously modeled. All these detail modeling helped the aerodynamic model to systematically validate with not only time averaged forces, but also time-history of aerodynamic forces obtained from in-house experiments. Once validated, the aerodynamic model is utilized to understand the physics behind the force production of cycloidal rotor. Through systematic investigation, it was observed that the dynamic virtual camber effect plays a very important role in this aspect. Dynamic virtual camber due to pitch rate creates asymmetry in side-force between the right and the left halves, which in turn causes net time averaged side force on a cycloidal propeller in hover even with zero phase offset. Moreover, it is found extremely crucial for a cycloidal rotor to rotate in opposite direction (back-spin) with respect to the incoming flow in order to produce an upward vertical force in forward flight. This is due to the dynamic nature of virtual camber effect. Although the above mentioned lower order model is computationally inexpensive and capable of predicting rotor performance with sufficient accuracy, it cannot accurately capture the complex flow-field of cycloidal rotor, specifically the blade vortex interaction and geometry of trailing vortices. For this reason, a high-fidelity model of cycloidal rotor based on free-wake is developed to further investigate aerodynamics of cycloidal rotor in more detail. The prediction of the developed free wake model shows even better correlation with in-house experimental data compared to that of a lower model. Although, wake model is much more expensive from computational point of view which limits its application for preliminary design optimization of cycloidal rotor. Experimental study shows that cycloidal rotor goes through large blade deflections mainly due to centrifugal force which decreases thrust production and increases power requirement of the rotor. To capture these deflections, a fully nonlinear geometrically exact model is developed which shows much better prediction compared to a traditional 2nd order nonlinear model. To investigate effect of blade deflections on cycloidal rotor performance an aeroelastic framework of cycloidal rotor is developed by coupling lower order unsteady aerodynamic model with the structural model. The experimental validation shows inclusion of geometrically exact model is crucial for accurate performance prediction of flexible cycloidal rotors. Through systematic investigation utilizing the aeroelastic model, it is observed that nonlinear moment, arising due to coupling of bending curvatures in two orthogonal directions, is the key reason behind performance drop of flexible rotors. To obtain performance of conventional nose rotor in low Reynolds number regime, a modified blade element momentum theory based model is developed which utilizes look-up table obtained from CFD study. Both CFD look-up table and model predictions are validated with previously published experimental data. Control strategy of a cycloidal rotor based MAV, known as ‘Cyclocopter’ is developed for different flight conditions. Based on that, a coupled trim analysis of cyclocopter is performed for by simultaneously solving blade response equations and vehicle trim equations. Once systematically validated with in-house experimental data, the coupled trim model is utilized to investigate effect of several design parameters on the control inputs of the vehicl

Aeronautical engineering: A continuing bibliography with indexes (supplement 201)

This bibliography lists 438 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1986

Planification de trajectoire et contrôle d'un système collaboratif : Application à un drone trirotor

This thesis is dedicated to the creation of a complete framework, from high-level to low-level, of trajectory generation for a group of independent dynamical systems. This framework, based for the trajectory generation, on the resolution of Burgers equation, is applied to a novel model of trirotor UAV and uses the flatness of the two levels of dynamical systems.The first part of this thesis is dedicated to the generation of trajectories. Formal solutions to the heat equation are created using the differential flatness of this equation. These solutions are transformed into solutions to Burgers' equation through Hopf-Cole transformation to match the desired formations. They are optimized to match specific requirements. Several examples of trajectories are given.The second part is dedicated to the autonomous trajectory tracking by a trirotor UAV. This UAV is totally actuated and a nonlinear closed-loop controller is suggested. This controller is tested on the ground and in flight by tracking, rolling or flying, a trajectory. A model is presented and a control approach is suggested to transport a pendulum load.L'objet de cette thèse est de proposer un cadre complet, du haut niveau au bas niveau, de génération de trajectoires pour un groupe de systèmes dynamiques indépendants. Ce cadre, basé sur la résolution de l'équation de Burgers pour la génération de trajectoires, est appliqué à un modèle original de drone trirotor et utilise la platitude des deux systèmes différentiels considérés. La première partie du manuscrit est consacrée à la génération de trajectoires. Celle-ci est effectuée en créant formellement, par le biais de la platitude du système considéré, des solutions à l'équation de la chaleur. Ces solutions sont transformées en solution de l'équation de Burgers par la transformation de Hopf-Cole pour correspondre aux formations voulues. Elles sont optimisées pour répondre à des contraintes spécifiques. Plusieurs exemples de trajectoires sont donnés.La deuxième partie est consacrée au suivi autonome de trajectoire par un drone trirotor. Ce drone est totalement actionné et un contrôleur en boucle fermée non-linéaire est proposé. Celui-ci est testé en suivant, en roulant, des trajectoires au sol et en vol. Un modèle est présenté et une démarche pour le contrôle est proposée pour transporter une charge pendulaire

Experimental Investigation of a MAV-Scale Cyclocopter

The development of an efficient, maneuverable, and gust tolerant hovering concept with a multi-modal locomotion capability is key to the success of micro air vehicles (MAVs) operating in multiple mission scenarios. The current research investigated performance of two unconventional cycloidal-rotor-based (cyclocopter) configurations: (1) twin-cyclocopter and (2) all-terrain cyclocopter. The twin-cyclocopter configuration used two cycloidal rotors (cyclorotors) and a smaller horizontal edge-wise nose rotor to counteract the torque produced by the cyclorotors. The all-terrain cyclocopter relied on four cyclorotors oriented in an H-configuration. Objectives of this research include the following: (1) develop control strategies to enable level forward flight of a cyclocopter purely relying on thrust vectoring, (2) identify flight dynamics model in forward flight, (3) experimentally evaluate gust tolerance strategies, and (4) determine feasibility and performance of multi-modal locomotion of the cyclocopter configuration. The forward flight control strategy for the twin-cyclocopter used a unique combination of independent thrust vectoring and rotational speed control of the cyclorotors. Unlike conventional rotary-winged vehicles, the cyclocopter propelled in forward flight by thrust vectoring instead of pitching the entire fuselage. While the strategy enabled the vehicle to maintain a level attitude in forward flight, it was accompanied by significant yaw-roll controls coupling and gyroscopic coupling. To understand these couplings and characterize the bare airframe dynamics, a 6-DOF flight dynamics model of the cyclocopter was extracted using a time-domain system identification technique. Decoupling methods involved simultaneously mixing roll and yaw inputs in the controller. After implementing the controls mixing strategy in the closed-loop feedback system, the cyclocopter successfully achieved level forward flight up to 5 m/s. Thrust vectoring capability also proved critical for gust mitigation. Thrust vectoring input combined with flow feedback and position feedback improved gust tolerance up to 4 m/s for a twin-cyclocopter mounted on a 6-DOF test stand. Flow feedback relied on a dual-axis flowprobe attached to differential pressure sensors and position feedback was based on data recorded by the VICON motion capture system. The vehicle was also able to recover initial position for crosswind scenarios tested at various side-slip angles up to 30 degrees. Unlike existing multi-modal platforms, the all-terrain cyclocopter solely relied on its four cyclorotors as main source of propulsion, as well as wheels. Aerial and aquatic modes used aerodynamic forces generated by modulating cyclorotor rotational speeds and thrust vectors while terrestrial mode used motor torque. In aerial mode, cyclorotors operated at 1550 rpm and consumed 232 W to sustain hover. In terrestrial mode, forward translation at 2 m/s required 28 W, which was an 88% reduction in power consumption required to hover. In aquatic mode, cyclorotors operated at 348 rpm to achieve 1.3 m/s translation and consumed 19 W, a 92% reduction in power consumption. With only a modest weight addition of 200 grams for wheels and retractable landing gear, the versatile cyclocopter platform achieved sustained hover, efficient translation and rotational maneuvers on ground, and aquatic locomotion

NAVIGATION AND AUTONOMOUS CONTROL OF MAVS IN GPS-DENIED ENVIRONMENTS

Ph.DDOCTOR OF PHILOSOPH